Cellular phone users (especially younger users) increasingly communicate via short message service (SMS) text messaging instead of placing telephone calls. Although emergency call systems (e.g., 9-1-1, 1-1-2, 9-9-9) do not support SMS, there is an expectation by many users that “text to 9-1-1” functionality has been incorporated into text messaging networks already.
In many circumstances, sending an SMS text message to 9-1-1 would be less effective or less efficient than placing a phone call. Of course, SMS text messages require that messages be typed so as to be communicated over a network, whereas a voice call occurs in real time. Accordingly, voice calls can be more effective for quickly communicating an emergency to an emergency call center. But, there are some emergency circumstances where texting is necessary, such as instances when a user may not be able to speak, but may be capable of sending text messages.
The infrastructure for known emergency call systems has been designed for handling voice calls, rather than a text-based interface. FIGS. 1A-1C are block diagrams that illustrate conventional arrangements of components in present emergency call systems for handling emergency voice calls. The block diagrams illustrate conventional signaling paths between landline, mobile, and voice over Internet protocol (VoIP) telephones and a public-safety answering point (PSAP), which is call center responsible for answering calls to an emergency telephone number for police, firefighting, and ambulance services.
FIG. 1A illustrates a conventional landline emergency call system 1a. Landline telephones 11 establish calls by connecting to a local exchange 21. The local exchange 21 is a telephony switch that performs switching functions for landline telephones connected to the local exchange 21. The local exchange 21 identifies calls addressed to 9-1-1 and routes these calls to a 9-1-1 selective router (SR) 70 as a typical voice call using the SS7 signaling protocol. The 9-1-1 SR 70 then routes the emergency call to PSAP 80 using multi-frequency (MF) tone signaling. Here, the 9-1-1 SR 70 also identifies the appropriate PSAP 80 to receive the call. To do so, the 9-1-1 SR 70 maintains a table assigning a PSAP to each of landline telephones 11. During an emergency call, a call taker at PSAP 80 may require the caller's location to dispatch emergency services to the caller. In order for the PSAP 80 to determine the caller's location, the PSAP 80 can query the automatic location identification system (ALI) 92. The ALI 92 is one or more computers containing a database that stores the street address of every landline telephone.
FIG. 1B is a block diagram that illustrates a conventional signaling path between mobile user equipment (UE) and a PSAP. The conventional emergency call system for cellular telephone systems was developed to work within the already developed landline emergency call system 1a. 
In the conventional cellular emergency call system 1b depicted in FIG. 1B, the UE 10 communicates with a mobile switching center (MSC) 20 through a base station (not shown). Typically, the UE 10 is a cellular telephone, smartphone, or the like. The MSC 20 is a server or a plurality of servers that performs switching and management functions for UEs connected to a cellular network. The MSC 20 identifies calls addressed to 9-1-1 and routes these calls to a mobile positioning center (MPC) 91. The MPC 91 is a server or plurality of servers dedicated to assisting placement of emergency calls. Upon being notified of a call addressed to an emergency number (9-1-1), the MPC 91 determines an appropriate PSAP 80 to receive the emergency call based on the UE's location (as discussed below). The MPC 91 then instructs the MSC 20 to route the call to 9-1-1 SR 70 as a typical voice call using the SS7 signaling protocol. The 9-1-1 SR 70 then routes the emergency call to the PSAP 80 using MF signaling.
The MPC 91 also allocates a 10 digit number to the UE 10. The number is called a “pseudoANI” or “pANI”, which has an area code appropriate for the PSAP 80. The actual telephone number of the UE 10 cannot be used because the PSAP 80 does not support non-local area codes. The pANI is needed because a UE in a cellular network is mobile and may often be at a location where the telephone number associated with the UE is a non-local telephone number. The MPC 91 maintains a pool of such area-code appropriate pANIs for each PSAP. When a call arrives for the PSAP, one of the pANIs from the pool associated with the PSAP is allocated for use during the emergency call. When the call is over, the pANI is returned to the pool, and may be reused for another call to the same PSAP.
The MPC 91 and PSAP 80 are each connected to ALI 92. To request the caller's location, the PSAP 80 sends a query message to the ALI 92 using the pANI assigned to the call. The ALI 92 sends the query message to the MPC 91. The MPC 91 communicates with the PDE 93 in order to obtain the location of a UE. The PDE 93 is a cellular network element that obtains location measurements from the UE 10, such as global position system measurements, or from various forms of triangulation from the cellular towers to determine the latitude and longitude of the UE 10.
A rough location of a caller may also be determined using the cell ID, which includes the cell and sector currently serving the UE 10. Mobile emergency calls are typically routed based on the cell ID, and not necessarily on the closest PSAP to the user or the tower. A database that stores cell IDs and corresponding PSAPs is maintained at the MPC 91. The MPC 91 determines an appropriate PSAP to receive the emergency call by retrieving the PSAP 80 from the database based on the UE's serving cell ID.
FIG. 1C is a block diagram that illustrates a conventional signaling path between a VoIP telephone 12 and a PSAP. The conventional emergency call network for VoIP phone systems was also developed to work within the already developed landline emergency call network 1a. 
In the conventional VoIP emergency call system 1c depicted in FIG. 1C, the VoIP telephone 12 communicates with a call server 22 through an Internet connection. The call server 22 is a server or a plurality of servers that performs switching functions for VoIP telephones connected within the VoIP telephone network. The call server 22 identifies calls addressed to 9-1-1 and routes these calls to a voice over IP positioning center (VPC) 50. The VPC 50 is a server or plurality of servers dedicated to receiving emergency calls from the call server 22 using VoIP. Upon receiving a call addressed to an emergency call center, the VPC 50 determines an appropriate PSAP 80 to receive the emergency call based on the UE's location (as discussed below). The VPC 50 then routes the call to an emergency services gateway (ESGW) 60. The ESGW 60 is a gateway that receives the emergency call using VoIP and routes the call to a 9-1-1 SR 70 as a typical voice call using the SS7 signaling protocol. The 9-1-1 SR 70 then routes the emergency call to the PSAP 80 using MF signaling.
The VPC 50 also allocates a pANI to the UE 10. As is the case with cellular phones, a pANI is needed because the actual telephone number of the VoIP telephone cannot be used because the PSAP 80 does not support non-local area codes. The pANI is needed because a VoIP telephone may be at a location where the telephone number associated with the VoIP telephone is a non-local telephone number.
To request the caller's location, the VPC 50 sends a query to the location information server (LIS) 94. The LIS 94 is one or more servers containing a database that stores the street address of every VoIP telephone. The VPC 50 and PSAP 80 are each connected to the ALI 92. The PSAP 80 can also query the caller's location. To do so, the PSAP 80 sends a query message to the ALI 92 using the pANI assigned to the VoIP telephone 92. The ALI 92 sends the query message to the VPC 50. The VPC 50 relays the query to the LIS 94 in order to obtain the location of a VoIP telephone 12.
The infrastructure for known emergency call systems has been designed for handling voice calls, rather than a text-based interface. As an exception, emergency 9-1-1 systems accommodate use of text telephones (TTY), also known as text devices for the deaf (TDD), to enable allows deaf persons to contact emergency call centers. TTYs are text devices that use conventional analog telephone lines, and encode text on an analog phone call using tones, such as Baudot tones. In this manner, TTYs use tones on regular voice calls to convey text on an emergency voice call. A TTY uses a Baudot code or another code such as ASCII, sent by a 45.45 bps binary frequency-shift-keyed scheme that is carrierless, half duplex, and without error protection. All emergency call centers have one or more TTYs (as required by the Americans with Disabilities Act), and many have the capability to receive TTY calls at every call taker's position in the call center, although the use of TTY by the deaf is currently being phased out with other advances in technology.
Since existing emergency call centers are not able to accept SMS communications, upgrading the centers themselves to provide “text-to-9-1-1” functionality would be expensive and would require years of time for deployment. Therefore, it is desirable to provide an arrangement that enables texting of SMS messages to PSAPs without requiring upgrades of the emergency call centers themselves.
Accordingly, certain embodiments of the present invention are directed to systems and methods for delivering SMS and other media to call centers, including emergency call centers, which utilize existing infrastructure. Embodiments of the invention can use TTYs in the PSAPs to provide SMS capability in the UEs by interworking the SMS message system with the TTY support system in the emergency call process, thus allowing a wireless caller to text to the PSAP in the same way the caller would text to anyone else, which then allows the PSAP to use its TTY in the same way as any other TTY call.